Walter Anthony's Purple Nurple Optical Illusion

Epicharmus, a Greek poet and originator of Sicilian Comedy is credited to have said that "the mind sees and the mind hears. The rest is blind and deaf." Although Epicharmus' idea was conceived around 450 BC, it is interesting to apply it to our modern understanding of optical illusions, if we understand an optical illusion to mean a "false visual perception."

An optical illusion (also called a visual illusion) is characterized by visually perceived images that are deceptive or misleading. The information gathered by the eye is processed by the brain to give a percept that does not tally with a physical measurement of the stimulus source.

Below is Walter Anthony's "Purple Nurple Optical Illusion." Keep in mind that this is a static image. It is not animated in any way, but as your vision moves back and forth the center area seems to be moving toward the center (contracting) and the outer edges seem to be moving away (expanding) from the center. Also worth noting is that if you fixate on a point in the center and don't move your eyes this anomalous motion will stop.

Walter Anthony's website: http://opticalillusions4kids.blogspot.com